[mythtv-users] How do master and slave backends divide up work?

David George david at thegeorges.us
Fri Jan 4 17:04:12 UTC 2008

On 01/04/2008 10:36 AM, Ma Begaj wrote:
> I am thinking about building 2nd backend/frontend box.I have already
> have one backend/frontend box.
> I was thinking about the following problem this morning:
> how to make both of the boxes be "independent" but still using the
> same database without having third machine for the database.
> that means that the database should be on both machines in some kind
> of RAID1 over the network and I thought that this could be done. maybe
> with rsync or something similar. or some kind of mdadm over network.
> is there something like that?
> but the problem is when the box with the newest data is offline. there
> is no way to have  correct data in the db...
> anyone with a creative idea? :)

drbd is network RAID 1.  You will need to have mysql on its own 
filesystem.  By doing this you will only have one mysql server active at 
a time, but you can use heartbeat to move the mysql server to the active 
machine.  I have done this with postgresql and it works well.  Never 
tried with mysql though.  If you are thinking of trying this you will 
want a dedicated Gigabit ethernet link between the two machines for 
heartbeat and drbd sync.  You will also need a virtual IP address that 
heartbeat moves between the two machines.  I haven't really thought this 
entirely through for mythtv, but I have done this in other projects.  A 
couple of things that crossed my mind.  Your mysql settings will need to 
be set to the virtual IP, while your frontend will want to use the 
backend's real IP.  Also, there is a time (maybe up to 20 seconds) that 
the mysql server will not be available while it is moving from the 
master to the standby server.  In the end, is it really worth the trouble?



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